Embodiments of the present invention are directed to electromagnetic interference shielding. More specifically, embodiments of the present invention are directed to an electromagnetic interference containment device.
Any device or system that generates an electromagnetic field has the potential to disrupt the operation of electronic components, devices, and systems in its vicinity. This phenomenon is known as electromagnetic interference or EMI. For example, the internal circuits of personal computers generate RF fields which can interfere with the effective performance of other electrical equipment nearby. Problems with EMI can be minimized by ensuring that electronic equipment is operated with a good electrical ground system and is properly shielded.
Most computer systems have connectors for a variety of peripheral devices such as printer ports, network interfaces, etc. In one type of computer system, a printed circuit assembly (PCA) is inserted into an expansion slot of a chassis. A bulkhead is coupled with the PCA and provides the means for rigidly coupling the PCA with the chassis. The connector is located on the edge of the PCA and extends through an opening in the bulkhead. Part of the design specification for such systems requires a specific separation tolerance between the connector and the bulkhead. This separation tolerance allows a range of motion between the two components. Usually, this separation tolerance allows an air gap between the connector and the bulkhead to exist through which EMI can leak and affect other electronic equipment.
One solution to prevent this EMI leakage has been to fit a thin sheet metal shield which closes the gap between the connector and the bulkhead. The main requirement of the shield is that it prevents EMI emissions from leaking and conducts them to the grounded chassis of the computer system via the bulkhead. Typically, an opening is created in the shield which is slightly smaller than the connector and the edges of the opening are cut to create a series of xe2x80x9cfingersxe2x80x9d around the periphery of the opening. When the shield is pressed onto the connector, the fingers bend around and contact the connector and, once the bulkhead is coupled with the PCA, conduct the EMI emissions to the chassis.
As technology trends are creating higher frequency computer components, higher frequency EMI emissions are generated. In order to effectively contain these higher frequency emissions, the fingers of the EMI shields must be moved closer together. However, fabricating EMI shields is becoming increasingly expensive. Specifically, the tooling costs associated with producing the smaller cut-outs is becoming too expensive relative to the actual value of the EMI shield itself. The high investment in tooling also makes it difficult to prototype different designs or make changes to the existing design. Furthermore, the fingers are now so small and delicate that handling and installation of the EMI shield is difficult. Specifically, the force needed to insert the shield onto the connector often bends or breaks the smaller fingers which renders the EMI shield useless. Additionally the smaller fingers are so thin that a user can easily be cut by the EMI shield when handling it.
Another problem associated with sheet metal EMI shields is that they can not easily accommodate different separation tolerances and minimum compression requirements throughout the EMI shield. For example, the separation tolerance between the bulkhead and the PCA may be 0.6 mm, while the separation tolerance between the bulkhead and the chassis may be 1.2 mm or larger. Generally, the tooling used to fabricate EMI shields can not accommodate these different tolerances. Therefore, the EMI shield is fabricated using an average value of the two tolerances. This can result in an excessively tight fit between the PCA and the bulkhead, while the fit between the bulkhead and the chassis is not tight enough to prevent EMI leakage.
In one embodiment, a layer of compressible material is disposed between an electromagnetic interference source and a bulkhead coupled to the electromagnetic interference source. The layer of compressible material has a first thickness and a second thickness. A first layer of conductive material is disposed on the back side of the layer of compressible material and is electrically coupled to the electromagnetic interference source. The first layer of conductive material is for absorbing electromagnetic emissions from the electromagnetic interference source. A second layer of conductive material is disposed on the front side of the layer of compressible material and is electrically coupled to the first layer of conductive material. The second layer of conductive material is for electrically contacting the bulkhead and for conducting the electromagnetic emissions to the bulkhead.